The invention generally relates to fans for use in cooling systems. The invention relates particularly to a seal structure in a gap between the shroud and rotor of the fan to reduce noise by removing the swirling components of air flow at the tip region of fan blades and to minimize air leakage across the gap resulting in fan efficiency gains.
A pressure gradient between the pressure side and the suction side of a fan tends to create air leakage at the tip of fan blades. Conventionally, in axial flow fans, tip seals of a labyrinth type have been used to reduce tip air leakage or the flow of air in a gap (on the order of 5 mm) between the shroud and rotor. Ribs have also been used in an effort to reduce this air leakage. A disadvantage of the labyrinth seal is that this seal is difficult to manufacture and that often the axial constraints of the vehicle limit the proper design of the seal. Ribs in the tip region only prevent the swirling component of the flow from causing turbulence by reentering the fan. However, the ribs do not seal the air leakage through the tip gap effectively.
Another common method of reducing tip air leakage is to employ a band connecting the fan blades at the tips thereof. However, due to manufacturing limitations, the radial gap between the stationary shroud and the rotating band is usually on the order of 5 mm which limits the effectiveness of such a seal. Furthermore, the rotating band introduces a swirling component on the leakage flow that tends to increase fan noise.
Accordingly, there is a need to provide a seal structure to decrease the gap between a band of a rotor and shroud and to remove the swirling components of flow in the tip region of a fan so as to reduce noise with marginal losses in static efficiency.
An object of the invention is to fulfill the need referred to above. In accordance with the principles of the present invention, this objective is achieved by providing a turbomachine for moving air. The turbomachine includes a shroud disposed about an axis. The shroud has a pair of opposing faces defining a gap therebetween. The opposing faces are disposed generally transversely with respect to the axis. A rotor assembly is mounted for rotation about the axis. The rotor assembly has a plurality of blades with tips of the blades being coupled to an annular band. At least a portion of the annular band is disposed in the gap. Seal structure extends from each opposing face of the shroud and into the gap to reduce swirl and minimize air leakage across the gap.
In accordance with another aspect of the invention, a method of reducing effects of air flow between a shroud and a rotor assembly is provided. The shroud is disposed about an axis and has a pair of opposing faces defining a gap therebetween. The opposing faces are disposed generally transversely with respect to the axis. The rotor assembly is mounted for rotation about the axis. The rotor assembly has a plurality of blades with tips of the blades being coupled to an annular band. At least a portion of the annular band is disposed in the gap. The method provides seal structure extending from each opposing face and into the gap to reduce swirl and minimize air leakage across the gap.
Other objects, features and characteristics of the present invention, as well as the methods of operation and the functions of the related elements of the structure, the combination of parts and economics of manufacture will become more apparent upon consideration of the following detailed description and appended claims with reference to the accompanying drawings, all of which form a part of this specification.